Standardization of T‐cell depletion in HLA matched bone marrow transplantation

Summary. The IBM 2991 Blood Cell Processor has been used to isolate a mononuclear cell (MNC) fraction from the marrow of 31 allogeneic donors. The MNC fraction was then incubated with a combination of two murine monoclonal antibodies MBG6 (CD6) and RFT8 (CD8) followed by two rounds of treatment with rabbit complement resulting in a marrow inoculum significantly reduced in the number of T‐lymphocytes. We report here new specifications for the use of Ficoll‐Metrizoate, the method used to calculate T‐lymphocyte depletion and the details of our attempts to improve T‐depletion. Following marrow transplantation with this T‐depleted fraction, 29 patients are evaluable for engraftment, one patient failed to engraft and one died too early for evaluation. Twenty‐two had no acute graft‐versus‐host disease (aGvHD), at a minimum of 60 d, six had grade I acute GvHD and one grade III. No correlation was found between the absolute number of MNC infused and time to engraftment, nor any relationship between the number of residual viable T‐lymphocytes in the infused marrow and the incidence of GvHD, but the patient with the most severe aGvHD also had the highest number of T‐lymphocytes infused.